1. Field of the Invention
This disclosure relates to the field of illumination, and more particularly to the field of illumination sources controlled by a computer.
2. Description of the Related Art
LED lighting systems are used in a variety of applications to provide light, including for illumination, display and indication. One method of operating an LED in these systems is through pulse width modulation (PWM). That is, the current through the LED is fixed at a desired level and the duration the LED is activated varies to generate the appearance that the LED is dimming or increasing in intensity. The human eye integrates light it receives, and if the LED is on for a very short period of time, the LED appears dim even though the LED was operated at its optimum current. Another method of operating LEDs is through analog techniques where the amplitude of either the voltage or the current is modulated to change the light output of the LEDs. There are other techniques for operating LEDs, for example amplitude modulation of a pulsed signal or other techniques for modulating the power dissipated by the LED per unit of time. Certain techniques for the computer control of LEDs to generate illumination are disclosed in U.S. Pat. No. 6,016,038, which is hereby incorporated by reference.
One of the problems with changing the apparent or actual light output of an LED from a low light level to a higher light level is that the output changes may appear as stepped function rather than a smooth transition. This is common to other light sources, besides LEDs, as well. This is because the eye is highly sensitive to discrete changes in light output at low light levels. When the light is changed from one low light output level to another low light output level, the eye perceives the change as stepped. It would be useful to provide a lighting system that reduced the apparent stepped transition in light output from such a lighting system.